So, for the Suzuki reaction, we have our 3 noticeable steps involved in the catalytic cycle: oxidative addition, transmetalation, and reductive elimination. Now with oxidative addition, it involves the addition of the carbon halide to the transition metal complex. So our transition metal, palladium, has a lone pair from its d orbital well. So we're going to have here palladium, still connected to its 2 original ligands, connected to X, and also connected to R₁.
When we go into step 2, where we are dealing with transmetalation, the R₂ group transfers from our organoborane or boron compound to the palladium metal complex. So what happens here is that this bond breaks, attaches to the palladium, and at the same time, the halogen leaves and attaches to the boron portion. So what we get here at this point is we're going to have palladium, still connected to its 2 original ligands, connected to R₁ and now connected to R₂. And then as our waste material we have B(Y₂), and then the X that has just joined it.
Now with reductive elimination, we're going to create the connection between R₁ and R₂ and regenerate the palladium catalyst. So we're going to take this compound here and bring it down to show this process. Okay. So here it goes. What happens here is the R₁ group's going to attach to R₂, and then the bond is going to break and go to palladium. So what we're going to get now is we're going to get R₁ being connected to R₂, plus the regeneration of my palladium catalyst.
Remember, the two driving forces for a lot of these coupling reactions are to create a more conjugated product—we do that in the form of R₁ connecting to R₂—and also for us to follow the 18 or 16 electron rule for the transition metal. At this point, by giving up R₁ and R₂, palladium is no longer following the 18 or 16 electron rule. So it wants the reaction to continue again. The regeneration of the catalyst is basically a key factor that wants us to continue doing this reaction over and over again, which is why it's involved in a catalytic cycle. But just remember, when it comes to this basic Suzuki coupling reaction, remember we have a carbon halide and from the carbon halide we lose our X group, and then we have an organoborane or boron compound where we lose the BY₂ group. They are lost as a byproduct, and then R₁ and R₂ combine together to give us our coupling product at the end.